The weaving machines which are controlled by means of dobbies are constantly being further developed with respect to higher operating needs. The mass accelerations of the heddle frame result in higher forces acting onto the control members and an increased demand for a playfree operation.
These strong stresses which occur in the positive dobbies of the Hattersley construction lead to a quick wear at the ends of the baulk. It has been heretofore suggested to provide the ends of the baulks with reinforcing elements, for example in the form of ring segments, which serve to absorb the occurring support forces. These ring segments on the baulk ends are caught and held during the control period between the stop rails and the repulsion knives. Movements are thereby detected at the ends of the baulk, which movements result in a quick wear in the case of heavily stressed machine parts. The cause for this lies, on the one hand, in the complex construction of the draw hook baulk end not being able to be manufactured sufficiently exactly in the common form and at a reasonable expense and this, therefore, results in a nonpermissible play relative to the stop rail and the repulsion knife and the draw and support knife. As a result, impacts which occur due to the relative movement between the parts lead to an excessive overload of the machine parts. On the other hand, the ring segments cause at the ends of the baulk, due to the line contact point to the stop rail and to the repulsion knife, a specific load to be applied, through which common building materials are overloaded. Simultaneously with the creation of these high specific surface pressures, the lubricating film is pierced at the contact points. Soon dents occur due to a plastic deformation of the material and a material removal at the contact points occurs due to the lack of lubrication at these points. Due to the complex forms and relative movements, the wear continues in an accentuated manner. This wear leads first to unsteady frame movements and requires then the replacement of the worn parts, which results in undesirable interruptions in the operation.
The purpose of the invention is to reduce the friction path and the specific load and initial play which exists due to inexactnesses.
This is inventively achieved in the above-mentioned dobby by the external part of the bearing ends of the controllable draw hooks resting directly against the stop rails or repulsion knives, which causes the bearing ends to be caught during the control period of the draw hooks between the stop rail and the repulsion knife. The bearing end of the draw hook thus contacts the stop rail and the repulsion knife instead of the ends of the baulk. In the normal position, the bearing end of the draw hook is caught playfree between these two parts, which causes the draw hook to be held stationarily.
The inventive arrangement attains the purpose of facilitating a construction of the sensitive part in the dobby in such a manner that a more exact manufacture with a smaller initial play becomes easily attainable and that the support point between the end of the baulk and the stop rail or the repulsion knife results in a smaller specific stress and a simultaneously reduced friction path. At the same time, it became possible to shorten the swanneck between the bearing end of the draw hook and the elongated draw hook shaft, which swanneck was acted upon by the relatively voluminous ring segment, and to obtain a stronger form of the draw hook, which under a load tends to bend correspondingly less, namely elastically deforming along the length and thus forwards less interferingly movements to the weaving heddle frame.
This new arrangement results in the space between the stop rail and the repulsion knife (control period), the body of the draw knife and the repulsion knife and the support or holding knife and the stop rail being now occupied only by one and the same controllable individual element, namely the draw hook, wherein in place of the ring segment the outer surface of the bearing end of the draw hook rests directly selectively on the stop rail, the repulsion knife or during the control period on both simultaneously. The position of the bore in the bearing end may have a relatively large inexactness, without influencing the function of the machine. The outer form of the bearing end at the mentioned contact points may have a cylindrical or different convex form. In addition the outer form of the bearing end, in particular in the cylindrical version thereof, may be enclosed by a mounting shoe, for example of plastic, and rotatably limited with respect to the bearing end, which shoe is provided on the outside preferably with a surface, which forms an operative connection with the countersurface on the stop rail or the repulsion knife.